Someone that will suck the life out of a room full of generally happy people.
Commonly likened to an Atmosphere Vampire; they are fundamentally the same thing except the former does not bite!

An Atmosphere Vacuum is someone that in a conversation will have “apparently” done whatever you have done but better. A smug know-it-all with delusions of grandeur and other such narcissistic tendencies. The Atmosphere Vacuum is not happy unless interfering in other people’s business and is happiest when belittling others.

The Atmosphere Vacuum is dull, uninteresting, repetitive and completely unaware that they are hated due a lack of social awareness.

The presence of an Atmosphere Vacuum is likely to induce feelings of depression, anger, or mild nausea. Should be avoided at all costs.

"Look out everyone, Jackie is on her way !!! Every man for themselves"
Man what a atmosphere vacuum